1. Field of the Invention
This invention relates to an ink-jet recording apparatus having a detecting means for detecting an ink-pressure or an ink-residual quantity disposed to a part of an ink-supply system for supplying ink from an ink-reservoir to an ink-jetting system incorporated with ink-droplet jetting nozzles.
2. Description of the Prior Art
In an ink-jet recording apparatus, there are advantages that it is capable of not only recording at a high speed and with a very low noise but also using low-cost plain paper sheets and eliminating such a complicated step as development, fixation and the like. In addition, it is capable of making dot size and intervals relatively smaller so as to perform a highly sharp image recording, and is also effective to record Chinese characters, patterns and the like.
Concerning the recording heads for the ink-jet recording apparatuses, several types thereof have so far been developed and put into practice.
For example, as disclosed in Japanese Patent Examined Publication No. 12138/1978, the so-called "on-demand" type of ink-jet recording apparatuses have recently been developed and attracted attention. In this type apparatuses, ink-droplets are jetted through nozzles according to the change of each volume of pressure chambers every time when electric pulses are applied to a recording head in correspondence to every electric signal for recording.
One of the advantages of this on-demand type is that the amount of ink consumed may be economized, high reliability may be secured and the apparatus itself may also be made compact in size, light in weight and low in cost, because ink is jetted only when needed in correspondence to image signals so that no system for collecting ink may be required.
Another advantage thereof is that a high resolving power printing and a high speed printing may be performed and a colorized printing may also readily be made.
In addition to the above, there is another on-demand type ink-jet recording apparatus disclosed in Japanese Patent Examined Publication No. 35936/1979. This type has adopted therein such a system as loaded in a single recording head with a plurality of nozzles.
FIGS. 1 and 2 are a sectional view and a plain view respectively of the typically schematized illustration of this type.
FIG. 3 shows an ink-jet recording head concretely comprising seven units of nozzle series arranged according to the above-mentioned recording method.
In FIGS. 1 through 3, a plurality of nozzles 1, a plurality of pressure chambers 2 connected to the nozzles 1 respectively, and a common ink chamber 3 for commonly distributing ink supplied from ink-reservoir 7 into the pressure chambers 2, each of which is arranged onto the same plane so as to construct a recording head.
Ink for recording use is supplied through the ink-reservoir 7, filter 6, valve means 5, ink supply tube 4 and then to common ink chamber 3. The common ink chamber 3 is branched into a plurality of pressure chambers 2 each connected to a plurality of nozzles 1 each corresponding to image elements in the vertical direction of an image. A piezoelectric transducing element 8 connected electrically to an electron pulse generator 9 is attached to a part of the wall of each pressure chamber 2. The piezoelectric transducing element 8 is a flexible plate suitably capable of being flexible inward the pressure chamber 2 when it receives an electric signal generated from the generator 9. This element comprises, for example, a piezoelectric crystal and is attached to the outer wall of the pressure chamber with an electroconductive thin diaphragm.
In this method, the piezoelectric transducing element 8 is abruptly bent inward the pressure chamber 2 upon the receipt of an electric signal generated from the electron pulse generator 9. By the rapid reduction of the volume of pressure chamber 2 thus caused, ink inside the chamber is jetted out and flown in the form of ink-droplets from nozzle 1 to a facing recording paper to complate a dot-recording. The amount of ink reduced by being jetted out from pressure chamber 2 is replenished with ink flowed from common ink chamber 3 where the ink is stored into pressure chamber 2. The amount of ink reduced in common ink chamber 3 is detected as a pressure reduction by means of liquid pressure detecting means which are provided each to flexible diaphragm 10 made a part of the wall of common ink chamber 3 and to the outside of the flexible diaphragm 10, respectively. The liquid pressure detecting means comprises a long cantilever type beam 11 whose front end is attached to the displacement detection part of the flexible diaphragm 10 and strain gauge 12 provided to the base of the beam 11.
When the liquid pressure detecting means detects that the liquid pressure of common ink chamber 3 dropped to not higher than the specified lowest level, then an electric signal is dispatched to open valve means 5 and ink is introduced from the ink reservoir through ink supply tube 4 to common ink chamber 3. When the liquid pressure of common ink chamber 3 to be detected by the liquid pressure detecting means is raised to not lower than the specified highest level, then the value means is closed to stop the ink flow from ink reservoir 7 to common ink chamber 3. Thus, the liquid pressure of common ink chamber 3 is maintained constantly within the range between the highest level and the lowest level. In the state that the liquid pressure is within the range, ink droplets can be jetted out stably and continuously from nozzles 1.
In the meanwhile, the flexible diaphragm 10 is formed to serve as the upper wall of the common ink chamber 3 of the recording head by attaching it over to the opening of the common ink chamber 3 so as to cover the opening to tightly close the ink in the chamber 3. The volume of the common ink chamber 3 is so made large enough as to correspond to the changes of the volume of pressure chambers 2.
Common ink chamber 3 and flexible diaphragm 10 each are so constructed as to absorb the pressure of ink return caused by the deformation of pressure chambers 2 at the time when ink is filled therein and is jetted. In a multi-nozzle type recording head, the so-called channel interruption is caused in which a pressure wave generated from the pressure chamber 2 of a channel undulates to the pressure chamber 2 of another channel through the common ink chamber 3 to deteriorate the jet-flying performance of ink-droplets from the other channel. Te described common ink chamber 3 and flexible diaphragm 10 are capable of preventing such a pressure wave from passing around.
In such a recording head constructed as mentioned above, a constant liquid pressure of ink should be maintained in the recording head, however, there may be some instances where a liquid pressure is lowered by the following reasons:
Namely, ink pressure fluctuates much in a recording head because of the rapid change of the amount of ink consumed which is caused with the change of dot density at the time of recording, or of the change of the residual amount of ink in the ink reservoir. Because of this fluctuation of ink pressure level, it has been difficult to stabilize the flying performance of ink-droplets jetted from the nozzles. In the serious cases, there have been such instances where the replenishment of ink could not come level with the consumption thereof and air bubbles were inhaled from nozzles because the liquid pressure were lowered, so that an ink-jet recording has failed into trouble.
In a recording head in which ink is supplied by a hydrostatic pressure, when an ink reservoir and the recording head are connected by an ink supply system, the change of an ink volume is somewhat absorbed by ink traffic between the recording head and the ink reservoir, however, when the recording head is preserved independently after removing from a recording apparatus (e.g., a printer), ink overflows from the nozzles or air bubbles are inhaled from the nozzles, during preservation by the abovementioned temperature change or by evaporation, because the recording head is sealed at the ink entrance path so as not to inhale any air bubble.
Further, in the conventional hydrostatic pressure type ink supply systems in which an almost constant ink-pressure is maintained in a recording head, the height of an ink reservoir is fixed to the position of the recording head. It is, therefore, difficult to maintain a constant liquid pressure according to the changes in the amount of ink consumed, remained, and the like.
Also, in an ink-jet recording apparatus in which pressurized ink is supplied from an ink reservoir having a pressurizing means and the liquid pressure is adjusted by a valve means provided to the halfway of an ink supply system so as to supply ink into a recording head, or in another ink-jet recording apparatus in which ink is supplied, with a hydrostatic pressure, directly from an ink reservoir to a recording head, there are many cases where various difficulties are caused by such an ink pressure change as mentioned above. To cope these difficulties, a constant detection should be made on the liquid pressure of ink stored in a recording head, ink supply system or ink reservoir, and according to the detection signal such a measure as a liquid pressure control, a warning on a liquid pressure abnormality or a print-stoppage should be taken without delay.
In addition to the above, as shown in FIGS. 1 through 3, the liquid pressure detecting means comprising beam 11 and strain gauge 12 each provided onto a recording head has various disadvantages that the strain gauge performance scatter between the individual elements to make adjustment very difficult, the element change with the passage of time is serious, so that a compensation system should be required, the elements are too fine, so that the attachment thereof to the mechanism must need a high accuracy, the elements are expensive, so that the overall cost is raised, and the like.